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.TH Tss2_Tcti_Libtpms_Init 3 "FEBRUARY 2021" "TPM2 Software Stack"
.SH NAME
Tss2_Tcti_Libtpms_Init \- Initialization function for the libtpms TPM simulator TCTI library.
.SH SYNOPSIS
.B #include <tcti/tcti_libtpms.h>
.sp
.BI "TSS2_RC Tss2_Tcti_Libtpms_Init (TSS2_TCTI_CONTEXT " "*tctiContext" ", size_t " "*contextSize" ", const char " "*conf" ");"
.sp
The
.BR  Tss2_Tcti_Libtpms_Init ()
function initializes a TCTI context used to communicate with the libtpms TPM2
simulator.
.SH DESCRIPTION
.BR Tss2_Tcti_Libtpms_Init ()
attempts to dynamically load the libtpms library and initialize a caller allocated
.I tcti_context
of size
.I size
\&. Since the
.I tcti_context
must be a caller allocated buffer, the caller needs to know the buffer size
required by the TCTI library. The minimum size of this context can be
discovered by providing
.BR NULL
for the
.I tcti_context
and a non-
.BR NULL
.I size
parameter. The initialization function will then populate the
.I size
parameter with the minimum size of the
.I tcti_context
buffer. The caller must then allocate a buffer of this size (or larger) and
call
.B Tss2_Tcti_Libtpms_Init ()
again providing the newly allocated
.I tcti_context
and the size of this context in the
.I size
parameter. This pattern is common to all TCTI initialization functions. We
provide an example of this pattern using the
.BR Tss2_Tcti_Libtpms_Init ()
function in the section titled
.B EXAMPLE.
.sp
The
.I conf
parameter can be used to specify the path to a state file (or NULL for none).
.sp
Once initialized, the TCTI context returned exposes the Trusted Computing
Group (TCG) defined API for the lowest level communication with the TPM.
Using this API the caller can exchange (send / receive) TPM2 command and
response buffers with the libtpms TPM simulator. In nearly all cases however,
the caller will initialize a context using this function before passing the
context to a higher level API like the System API (SAPI), and then never touch
it again.
.sp
For a more thorough discussion of the TCTI API see the \*(lqTSS System Level
API and TPM Command Transmission Interface Specification\*(rq as published by
the TCG:
\%https://trustedcomputinggroup.org/tss-system-level-api-tpm-command-transmission-interface-specification/
.SH RETURN VALUE
A successful call to
.BR Tss2_Tcti_Libtpms_Init ()
will return
.B TSS2_RC_SUCCESS.
An unsuccessful call will produce a response code described in section
.B ERRORS.
.SH ERRORS
.B TSS2_TCTI_RC_BAD_VALUE
is returned if both the
.I tcti_context
and the
.I size
parameters are NULL.
.SH EXAMPLE
.sp
TCTI initialization fragment:
.sp
.nf
#include <inttypes.h>
#include <stdlib.h>
#include <stdio.h>
#include <tcti/tcti_libtpms.h>

TSS2_RC rc;
TSS2_TCTI_CONTEXT *tcti_context;
size_t size;

rc = Tss2_Tcti_Libtpms_Init (NULL, &size, NULL);
if (rc != TSS2_RC_SUCCESS) {
    fprintf (stderr, "Failed to get allocation size for libtpms TCTI "
             " context: 0x%" PRIx32 "\n", rc);
    exit (EXIT_FAILURE);
}
tcti_context = calloc (1, size);
if (tcti_context == NULL) {
    fprintf (stderr, "Allocation for TCTI context failed: %s\n",
             strerror (errno));
    exit (EXIT_FAILURE);
}
rc = Tss2_Tcti_Libtpms_Init (&tcti_context, &size, "tpm2-state.bin");
if (rc != TSS2_RC_SUCCESS) {
    fprintf (stderr, "Failed to initialize libtpms TCTI context: "
             "0x%" PRIx32 "\n", rc);
    free (tcti_context);
    exit (EXIT_FAILURE);
}
.fi
